Dispersants have been used in the construction industry to disperse cementitious mixtures. Dispersants such as sulfonated melamine formaldehyde condensate (SMF) and sulfonated naphthalene formaldehyde condensate (BNS) are commonly used as dispersants. However, these compounds require more than the desired amount of material to achieve a desired level of concrete workability or water reduction. In addition, these materials do not achieve full range (Type A to Type F) water reducing capability, as defined in ASTM C494.
It is important that dispersants be used in concrete situations where strength and durability are involved. Dispersants are a necessary component in high strength and high durability concretes. Due to the use of low water amounts in the high performance concretes, sometimes high dispersant amounts are necessary to achieve workable concretes. High BNS levels can lead to undesirable retardation of set and may not provide the required workability retention over time.
It is desirable to provide a material that is several times more efficient as a cement or concrete dispersant than the traditional materials like BNS and SMF. Improving efficiency reduces the amount of material required to achieve a desired level of concrete workability or water reduction. With respect to the presently used dispersants, BNS and SMF, it is also desirable to improve slump retention while maintaining normal setting characteristics. Providing a dispersant with full range (Type A to F) water reducing capability is also a desirable characteristic.
A cementitious mixture refers to pastes, mortars, and concrete compositions comprising a hydraulic cement binder. Cementitious mixtures may also include high percentages of pozzolan cement replacement. Pastes are defined as mixtures composed of a hydraulic cement binder, either alone or in combination with pozzolans such as fly ash, silica fume, or blast furnace slag, and water. Mortars are defined as pastes that additionally include fine aggregate. Concretes additionally include coarse aggregate. These compositions may additionally include other admixtures such as set retarders, set accelerators, defoaming agents, air-entraining or air detraining agents, corrosion inhibitors, water reducing agents, pigments, and any other admixture that does not adversely affect the advantageous results obtained by the admixtures of the present invention.
Certain prior art polymer dispersants have inadequate long term solution stability. As time progresses, these prior art polymers become less effective as a dispersant.
Over the years, the use of pozzolanic materials as a partial replacement for portland cement in concrete has become an increasingly attractive alternative to portland cement alone. The desire to increase the use of fly ash, blast furnace slag, and natural pozzolanic cement in concrete mixtures can be attributed to several factors. These include cement shortages, economic advantages of portland cement replacement, improvements in permeability of the concrete product, and lower heats of hydration.
The growth in the use of higher amounts of pozzolanic cement replacements, such as fly ash for example, in concrete has been impaired by the potential incompatibility exhibited by these materials, especially when used at high percentages, in combination with water reducing admixtures. Water reducers are desirable to decrease the amount of water required in the preparation of the cementitious mixtures, and to increase the strength of the resulting concrete. However, the incompatibility of the pozzolan replacement materials with certain water reducing admixtures can result in the significant retardation of the initial and final setting of the concrete containing both these materials.
Despite the cost and performance advantages of fly ash, slag, and natural pozzolans as partial replacements of portland cement in concrete, there are practical limitations to the amount at which they can be used in the cementitious mixture. Using these materials at higher levels, such as above about 10 to 15 weight percent based on the weight of the portland cement, can result in the retarded setting time of the concrete up to several hours, and perhaps longer depending upon the ambient temperature. This incompatibility puts a burden of increased costs and time on the end user which is unacceptable.
While it is known to use set time accelerators in concrete mixtures, these accelerator admixtures have been ineffective in solving the compatibility problem that exists in high pozzolan replacement/portland cement mixtures, particularly when used with water reducing admixtures, so that set time is not able to be decreased to an acceptable level. The use of accelerators with water reducers, such as naphthalene sulfonate formaldehyde condensates, lignin and substituted lignins, sulfonated melamine formaldehyde condensates and the like, has been ineffective to produce an acceptable high pozzolanic replacement containing hydraulic cement based cementitious mixture with normal setting characteristics and an acceptable resulting concrete.
U.S. Pat. Nos. 4,373,956 and 4,473,405 discloses various admixture compositions for incorporation into hydraulic cement mixes to accelerate the rate of hardening and setting. U.S. Pat. No. 4,337,094 discloses combinations of additives which can be used to accelerate the setting time of portland type cements. These additives, when used in cementitious mixtures containing portland cement and high proportions of pozzolan cement replacements, as well as a water reducer, cannot compensate for the retardation of setting time induced in the mixtures by the cement replacement and water reducer, and thus do not acceptably accelerate the mixture to setting.
U.S. Pat. No. 5,556,458 discloses a cementitious composition containing a high percentage of fly ash and hydraulic cement, but in which a fly ash containing a particular calcium oxide content is required and a water reducing admixture is not present. The composition is useful for quick setting repair mortar type products.
A cementitious dry cast mixture refers to pastes, mortars, and concrete compositions comprising a hydraulic cement binder having consistencies ranging from stiff to extremely dry as defined in ACI 211.3R, Table 2.3.1.
Cementitious dry cast mixtures are used to form many articles, for example, concrete pipe, roof tile, masonry units, paver units, extruded plank, and any other preformed cementitious articles, in a mold or from an extrusion die. Each of these applications has basic desired characteristics that are critical in terms of producing quality finished units.
In masonry block applications, production speed, sufficient green strength, and the ability to resist slumping, sagging or deforming when stripped from the mold is critical since stripping occurs immediately after casting. The same is true for concrete pipe or roof tile with the additional desired property of improved surface appearance with reduced surface imperfections and reduced roller and/or die wear on equipment producing extruded pieces.
It is desired to reduce the cycle time of the manufacture of each article. The reduction of cycle time reduces the cost of manufacture for each article and increases the number of articles that can be produced in a given time. Cycle time is defined as the time to complete one full cycle from the beginning of feed to the beginning of feed. The beginning of feed is when the dry cast mixture is fed from a collection hopper into the process. It is also desired to improve the compaction and consolidation of the cementitious dry cast mixture without altering the consistency of the mixture.
Green strength refers to the stability of the article in retaining its shape once the article is removed from the mold or extruder. Green strength is dependent on the consistency of the cementitious dry cast mixture, the amount of fines in the cementitious dry cast mixture, and the moldability of the cementitious dry cast mixture.
Currently, the water to cement (W/C) ratio used in present dry cast mixtures is from about 0.25 to about 0.40. It is desired to minimize the amount of water needed in a cementitious dry cast mixture to achieve consolidation and no sag or deformation in an article produced from the cementitious dry cast mixture.
Another limiting factor in the improvement of dry cast mixtures is the type and amount of dispersant used. Conventional dispersant chemistries such as naphthalene sulfonates, melamine sulfonates, and lignosulfonates have a lower limit to their effective dosage; below which they are not effective. At levels above the effective dosage of these dispersants, the dry cast mixture becomes critically sensitive to very slight changes in water or moisture content. This makes the use of these dispersants impractical.
A further limitation in the present art is the compressive strength of articles produced from cementitious dry cast mixtures. Compressive strength is directly related to the density of the article.
What is required by the industry, however, is a cementitious mixture capable of forming concrete with a dispersant that is more effective than SMF or BNS condensates at lower effective dosages and which provides Type A to Type F water-reducing effect. Also required by the industry is a cementitious mixture capable of forming concrete which contains a significant percentage of cement replacement material (to replace a portion of the hydraulic cement, such as portland cement) for performance and cost considerations, and water reducers to decrease water usage and increase compressive strength and durability, the components in such cementitious mixtures being compatible and which mixtures set in an industry-acceptable time period. Also required by the industry is a cementitious dry cast mixture containing a dispersant that has a low effective dosage, that is not critically sensitive to changes in water or moisture content, that functions in mixtures having a slump of less than about one (1) inch, that permits mixture consolidation and compaction in response to vibration energy, that has increased green strength and compressive strength, and that provides for reduced cycle time in the manufacture of articles from dry cast mixtures.
It is therefore an object of the invention to provide a cement or concrete dispersant that has increased solution storage life.
It is another object of the present invention to provide a cement or concrete dispersant material that is several times more efficient than the traditional dispersants such as BNS and SMF condensates.
It is another object of the present invention to provide a cement or concrete dispersant material with improved efficiency which reduces the amount of material required to achieve a desired level of concrete workability or water reduction.
It is another object of the present invention to provide a cement or concrete dispersant material to improve concrete slump retention while maintaining normal setting characteristics.
It is another object of the present invention to provide a cement or concrete dispersant material capable of providing a Type A to Type F water-reducing effect.
It is another object of the invention to provide a cementitious mixture which contains a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, as well as water reducing materials, which have acceptable or improved compressive strength.
It is another object of the invention to provide a cementitious mixture which contains a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, as well as water reducing materials, which set in an industry-acceptable time period.
It is another object of the invention to provide a method for preparing a cementitious material which contains a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, as well as water reducing materials, which have acceptable or improved compressive strength and which set in an industry-acceptable time period.
It is another object of the invention to provide a compatibilizing admixture for cementitious mixtures which contain a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, which admixtures provide water reducing means for imparting acceptable or improved compressive strength, and set accelerating means for inducing the mixture to set in an industry-acceptable time period.
It is another object of the invention to provide a cementitious dry cast mixture that consolidates and compacts in response to vibration energy.
It is another object of the invention to reduce the cycle time of manufacturing a cementitious dry cast mixture article to reduce the cost of manufacture of the article.
It is another object of the invention to provide a cementitious dry cast mixture article that has increased green strength and increased compressive strength.
It is another object of the invention to provide a cementitious dry cast mixture article that has increased density.
It is another object of the invention to provide a cementitious dry cast mixture that has improved surface appearance because the increased density and compaction reduces the air pockets and imperfections that form as a result of poor consolidation.
It is another object of the invention to provide sufficient dispersion of uncompacted silica fume or partially compacted silica fume in the cementitious dry cast mixture without altering the consistency of the mixture and without increasing the required water content of the mixture.